Cutting machines that include a rotatable knife holder to which are clamped a plurality of cutting knives are well known in the wood machining industry. Wood to be processed in the form of raw logs or processed lumber is fed into the cutting machines and the rotating knives rapidly convert the logs or lumber into chips, flakes, particles or other products. Examples of such machines used in the forest products industry include:
1) chippers and hogs used in saw mills, pulp mills, chipping plants and mobile units to make pulp chips or mulch; PA0 2) planners, matchers, milling machines and routers used in lumber mills to finish the surface of lumber or in manufacturing plants to shape wood; PA0 3) waferizers and flakers used to make particles or flakes for manufacture of wood products such as oriented strand board (OSB) and particle board.
The cutting machines described above employ numerous different configurations with respect to knife clamping arrangements, however, they are all governed by the same design considerations.
The knives are subjected to large centrifugal forces and the knife clamping force must be sufficient to retain the knives in place. Furthermore, in performing their cutting action, the knives tend to be pulled from or pushed into the knife clamp and the knife clamping force must be sufficient to overcome these forces. A safety hazard exists if knives come loose during operation of the cutting machine as the rotation speed of the knives tends to throw them outwardly with great force. In addition, the rotating knives often come into close proximity with stationary parts of the cutting machine and even slight movements of the knives can cause collisions and resulting catastrophic failure of the cutting machine.
The position and condition of the cutting knife edge is important in the cutting process. Particularly when flakes or chips are being formed, the position and sharpness of the knife edge is vital to the quality of product being produced. The knife edges dull and retract with use making it necessary to sharpen and reposition the knives periodically which requires stopping the cutting machine to gain access to the knives.
It is readily apparent from the foregoing discussion that cutting knife position is an important element of cutting machine design and operation. It is recognized that it would be advantageous to be able to monitor the position of the cutting knives in a cutting machine to prevent failures, to assist in scheduling of regular maintenance and sharpening of equipment and to ensure product quality. Visual inspection of the knives during operation is not possible as the configuration, presence of guard screens, size and rotating speed of cutting machines generally prevents an operator from observing the knives while the machine is working.